Add project files.

AssetStudio/ImportHelper.cs

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+using Org.Brotli.Dec;
+using System.IO;
+using System.IO.Compression;
+
+namespace AssetStudio
+{
+    public static class ImportHelper
+    {
+        public static FileReader DecompressGZip(FileReader reader)
+        {
+            using (reader)
+            {
+                var stream = new MemoryStream();
+                using (var gs = new GZipStream(reader.BaseStream, CompressionMode.Decompress))
+                {
+                    gs.CopyTo(stream);
+                }
+                stream.Position = 0;
+                return new FileReader(reader.FullPath, stream);
+            }
+        }
+
+        public static FileReader DecompressBrotli(FileReader reader)
+        {
+            using (reader)
+            {
+                var stream = new MemoryStream();
+                using (var brotliStream = new BrotliInputStream(reader.BaseStream))
+                {
+                    brotliStream.CopyTo(stream);
+                }
+                stream.Position = 0;
+                return new FileReader(reader.FullPath, stream);
+            }
+        }
+    }
+}